Technical Field
The present invention relates to a sintered body having a high translucency and thus suitable to make a Faraday rotator used in optical communication and optical measurement, and the Faraday rotator made of this sintered body and the invention also relates to a Faraday rotator made of this sintered body and an optical isolate containing such Faraday rotator.
Background Technology
In the applications of optical communication and optical measurement, when a light emitted from a semiconductor laser returns to the semiconductor laser, as it is reflected by a surface of a member put in the transmission path, the laser oscillation is destabilized. In order to intercept this reflection return light, an optical isolator has been used wherein the Faraday rotator rotates the polarization plane in non-reciprocal manner.
The optical isolator, as shown in FIG. 2, is mainly constituted by a Faraday rotator 1, a pair of polarizers 2, 2, one installed on a beam entrance side and the other on a beam exit side of the Faraday rotator 1, a magnet 3, and a ring 4 made of a stainless steel. The material to make this Faraday rotator 1 needs to have a high Faraday effect and a high transmittance with respect to the light of a wavelength to be used with.
In order to cope with the recent demand for the isolator to be further down-sized, the thickness of the Faraday rotator 1 need be made smaller, and hence the material to make such a thinner Faraday rotator should have a smaller optical attenuation effect and a higher transmittance. Heretofore, to answer this purpose a sintered material such as ytterbium oxide (Yb2O3) has been used.
For example in IP Publication 1, there is a description to the effect that a transparent oxide which contains ytterbium oxide (Yb2O3) by 30 mass % or more has a relatively large Verdet constant and exhibits scarce light absorption with respect to the light of a wavelength of 320-800 nm, so that the material is a suitable choice for down-sizing a Faraday rotator of an optical isolator.
However, a problem is pointed out with respect to the conventional material described in IP Publication 1, which is that its transmittance sharply drops with respect to lights that have wavelengths of 400 nm or shorter. In particular, if a Faraday rotator is made of the conventional material, the transmittance of a light of 325 nm-wavelength turns 50% or lower; what is worse, the material scarcely transmits shorter-wavelength lights.